One of the issues I had was determining which overloads add this configuration option to. There is:
        public static IAppBuilder MapHubs(this IAppBuilder builder);
        public static IAppBuilder MapHubs(this IAppBuilder builder, string path);
        public static IAppBuilder MapHubs(this IAppBuilder builder, IDependencyResolver resolver);
        public static IAppBuilder MapHubs(this IAppBuilder builder, string path, IDependencyResolver resolver);

Of course, there are equivalent methods for the SystemWeb host and memory host.

I discussed this with Damian, and he initially suggested having one overload that took single configuration object. He eventually decided that custom paths were common enough to warrant its own parameter (I don't feel strongly about this however). I'm not sure if he decided whether the resolver could go a configuration object, because in the end it was his suggestion to add the option to the IConfigurationManager.

Would you suggest using the following method signatures for MapHubs?
        public static IAppBuilder MapHubs(this IAppBuilder builder);
        public static IAppBuilder MapHubs(this IAppBuilder builder, MapHubsSettings settings);

        public class MapHubsSettings
        {
            public string Path { get; set; }
            public IDependencyResolver Resolver { get; set; }
 
            // I'm actually not sure if I like using the negative Disable instead of Enable,
            // but I like have the default value (false) to leave proxies enabled.
            public bool DisableJavaScriptProxies { get; set; }
        }